New Hampshire Senator Judd Gregg is being considered for the post of President Obama’s Commerce Secretary. And the implications and potential ramifications of such an appointment are that of political legend.

Gregg has been a staunch Republican for most of his career. The privileged son of a Republican dynasty (his father, Hugh Gregg, was governor and a leader of the New Hampshire GOP), Gregg was a tax lawyer when he first got on the public payroll with his 1979 election to the Governor’s Council. He then moved up through the U.S. House of Representatives (1981), Governorship (1989), and U.S Senate (1993). He’s been frequently denounced as insufficiently conservative, and has shown an occasionally abrasive personality (he once bitterly stated that Democratic opponent John Hoar was “appropriately named”). He’s also been a reliable Republican insider, a key advisor and ally of both Presidents Bush.

Now he’s being offered the only promotion from the Senate he’s likely to get: a cabinet position.

If Gregg accepts the position, the consequences could be severe for the Republicans. The Democrats hold 58 Senate seats, and appear to have a better-than-even chance of picking up a 59th in Michigan Minnesota. If Gregg were to resign, his seat would be filled by New Hampshire’s governor — Democrat John Lynch. That could mean the Democrats would then have the 60 seats they need to end filibusters. So Gregg’s departure could really hurt the Republicans.

On the other hand, Gregg could see this as his escape hatch. New Hampshire has grown increasingly Democratic over the past few years. In 2006, the Democrats not only picked up both U.S. House seats, they took the governorship and a majority in each House of the state legislature. In 2008, they kept the U.S. House and governorship, increased their majority in both state Houses, and took down Gregg’s colleague, John H. Sununu. Gregg remains the only Republican holding major office in New Hampshire, and that’s largely by default — he wasn’t up for re-election in 2006 or 2008.

But he will be in 2010, and the Democrats are already fighting over who will get to redecorate his office.

Gregg might very well see the writing on the wall. He could be coldly assessing his own situation (Gregg is famous for his cold-blooded analysis) and weighing his choice: two more years in the Senate as part of an embattled minority, or a turn in the Cabinet of President Obama for up to four years. To be one of a hundred Senators (and, even more relevant, one of the minority party), or one of fifteen Cabinet Secretaries and in the presidential line of succession (albeit in 10th place).

There are considerable machinations going on behind the scenes. There are rumors of talks with Governor Lynch to appoint a Republican to serve out the remaining two years of Gregg’s office, when it is likely that a Democrat will win anyway — while Gregg is definitely endangered, he is still a strong campaigner, and no potential Republican successor is seen as as much of a threat. Gregg is also being pressured by his fellow Senators to decline the position.

In the end, it all comes down to Gregg’s decision: which will benefit both him and his legacy? To bolt now, or risk ignominious defeat next year?

With Gregg, it’s almost impossible to predict.